Improving the Magnetoelectric Response of Laminates Containing High Temperature Piezopolymers

High magnetoelectric (ME) coefficients at room temperature have been found when 2-2 type laminates (one magnetostrictive, the other piezoelectric) made of iron-based Metglas alloys and PVDF piezoelectric polymer are used. Searching for a good ME response of such laminate composites when used at high temperatures, we have modified both constituents: first, by using magnetostrictive Metglas 2826 MB (with
$\lambda_{s}\approx 11\ {\rm ppm}$
) in the ribbon form thermally treated at high temperature, in order to get internal stress-relief conditions. The main consequence of such thermal treatment has been to achieve a piezomagnetic coefficient of
$d_{33}=1.5\times 10^{-6}/{\rm Oe}$
, higher than the measured one in the as-cast state for this alloy. As piezoelectric constituent, we have used a new class of high temperature piezopolymer: a series of nitrile containing polyimide copolymers were fabricated with a mixture of two aromatic diamines, namely 1,3-Bis-2-cyano-3-(3-aminophenoxy)phenoxybenzene (diamine 2CN) and 1,3-Bis(3-aminophenoxy)benzene (diamine 0CN). Those diamines were in 30/70, 40/60, and 50/50 proportions within the 0CN/2CN mixture. We have measured room temperature ME coefficients up to 0.37 V/cm.Oe, being this value directly correlated to the remnant polarization of each copolyimide.